1. Field of the Invention
The present invention relates to a digital recording apparatus and method, a digital reproduction apparatus and method, and a digital data conversion apparatus. More particularly, the present invention relates to a digital recording apparatus and method for converting sigma-delta (ΣΔ) modulated 1-bit digital audio data (1-bit data) into a PCM (Pulse Code Modulation) digital signal (PCM data) and recording it, to a digital reproduction apparatus and method for reproducing a recorded digital signal and obtaining the original 1-bit digital audio data, and to a digital data conversion apparatus.
2. Description of the Related Art
As apparatuses for recording and reproducing a video/audio signal, VTR apparatuses using video tape have hitherto been known. In recent years, digital VTR apparatuses for recording and reproducing digital video/audio data have come to be often used. Furthermore, apparatuses using a disk, a memory, or the like as a recording medium have been supplied. The sampling frequency of a digital audio signal in a digital video apparatus, such as such a digital VTR apparatus, is usually 48 kHz.
In comparison, in the case of a format of a CD (Compact Disc) or the like, with which an audio signal is converted into a digital form and recorded and reproduced, the sampling frequency is often 44.1 kHz. For example, in the CD-DA (Digital Audio) standard, a PCM (Pulse Code Modulation) digital signal (PCM data) having a sampling frequency of 44.1 kHz and having a number of quantization bits of 16 is used.
On the other hand, as another method for a digital audio signal, a method called sigma-delta (ΣΔ) modulation has been proposed in, for example, “AD/DA converter and digital filter”, The Journal of the Acoustical Society of Japan, Volume 46, No. 3 (1990), pp. 251 to 257. One-bit digital audio data (1-bit data) obtained by this ΣΔ modulation has a very high sampling frequency and a short data word length (for example, the sampling frequency is 64 times as high as 44.1 kHz and the data word length is 1 bit) in comparison with the format of data used for digital audio of a CD or the like of the related art, and has advantages such that a transmittable frequency band is wide.
Furthermore, even for a 1-bit signal, ΣΔ modulation enables a high dynamic range to be ensured in an audio band that is at a frequency lower than an oversampling frequency of 64 times higher. By utilizing this advantage, the method can be applied to recording and reproduction with high sound quality and data transmission.
This 1-bit ΣΔ modulated audio signal is used as a signal of a DSD (Direct Stream Digital) method in so-called super audio CD (SACD) as the next generation CD standard proposed by Sony Corporation and Philips Corporation.
As an example of the related art, Japanese Unexamined Patent Application Publication No. 9-261071 discloses a mastering apparatus for 1-bit digital audio data (1-bit data) of the DSD method. Japanese Unexamined Patent Application Publication No. 2001-5499 discloses a music data information transmission method and apparatus for digitally transmitting music data information, such as a sampling frequency of music data to be transmitted in digital music data transmission.